The field of this invention is cementing heads, particularly of the type used for the cementing of casing in a wellbore.
The production life of a well is directly affected by the quality of the cementing job. A good cementing job will seal off water zones, isolate producing intervals, control injected fluids during secondary recovery, control well stimulation treatments, protect the outside of the casing from corrosion, reduce the danger of a blowout caused by high pressure gas, help prevent loss of drilling mud up and around the outside of the casing and give added strength to the casing to help prevent collapsing due to external pressure. It is therefore extremely essential to have a good cement bond and uniform distribution of the cement on the outside diameter of the casing and on the inside of the wellbore. It must be free of any continuous channels or voids.
The fundamental concepts of displacing the mud or drilling fluid with a cement slurry is based upon a calculated volume of cement slurry being pumped down inside of the casing, out the bottom of the casing, and then up the annular space between the wellbore and the casing's outside diameter. For more efficient mud displacement, the techniques of centralizing the casing, attaching scratchers to the casing, conditioning the mud, proper cement mud density difference and pumping the cement in turbulent flow instead of laminar flow all promote more efficient mud displacement. However, even with these techniques, mud removal from the annular space between the wellbore and the outside diameter of the casing still prevents significant problems.
U.S. Pat. No. 3,777,819 discloses a technique of simultaneously rotating and reciprocating the casing string for the distribution of cement around the casing within the wellbore. The cementing head as disclosed in that patent has extensive external valving and by-pass manifolds which present manufacturing and operational problems.